/*
 * Javascript base64_encode() base64加密函数 用于生成字符串对应的base64加密字符串
 * @param string str 原始字符串
 * @return string 加密后的base64字符串
 */
function base64_encode(str){
    var c1, c2, c3;
    var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    var i = 0, len= str.length, string = '';
    while (i < len){
        c1 = str.charCodeAt(i++) & 0xff;
        if (i == len){
            string += base64EncodeChars.charAt(c1 >> 2);
            string += base64EncodeChars.charAt((c1 & 0x3) << 4);
            string += "==";
            break;
        }
        c2 = str.charCodeAt(i++);
        if (i == len){
            string += base64EncodeChars.charAt(c1 >> 2);
            string += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
            string += base64EncodeChars.charAt((c2 & 0xF) << 2);
            string += "=";
            break;
        }
        c3 = str.charCodeAt(i++);
        string += base64EncodeChars.charAt(c1 >> 2);
        string += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
        string += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6));
        string += base64EncodeChars.charAt(c3 & 0x3F)
    }
    return string
}
/*
 * Javascript base64_decode() base64解密函数 用于解密base64加密的字符串
 * @param string str base64加密字符串
 * @return string 解密后的字符串
 */
function base64_decode(str){
    var c1, c2, c3, c4;
    var base64DecodeChars = new Array(
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57,
        58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0,  1,  2,  3,  4,  5,  6,
        7,  8,  9,  10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
        25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
        37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1,
        -1, -1
    );
    var i=0, len = str.length, string = '';
    while (i < len){
        do{
            c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff]
        } while (
        i < len && c1 == -1
            );
        if (c1 == -1) break;

        do{
            c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff]
        } while (
        i < len && c2 == -1
            );
        if (c2 == -1) break;
        string += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));
        do{
            c3 = str.charCodeAt(i++) & 0xff;
            if (c3 == 61)
                return string;
            c3 = base64DecodeChars[c3]
        } while (
        i < len && c3 == -1
            );
        if (c3 == -1) break;
        string += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));
        do{
            c4 = str.charCodeAt(i++) & 0xff;
            if (c4 == 61) return string;
            c4 = base64DecodeChars[c4]
        } while (
        i < len && c4 == -1
            );

        if (c4 == -1) break;

        string += String.fromCharCode(((c3 & 0x03) << 6) | c4)
    }
    return string;
}